Three-dimensional semiconductor mounting has become essential for higher density and larger capacity. The three-dimensional mounting technique is a semiconductor production technique for thinning a semiconductor chip and connecting the chip to another chip by a through silicon via (TSV) to form a multilayer. To realize this technique, steps of grinding a non-circuit-forming surface (also referred to as “back surface”) of a substrate on which a semiconductor circuit has been formed to thin the substrate, and then forming an electrode including a TSV on the back surface, are required. In the step of grinding the back surface of a silicon substrate, a protective tape for the back surface is conventionally attached to a back side of the surface to be ground to prevent the wafer from breaking during grinding. However, this tape uses an organic resin film as its supporting base, which has flexibility, but inadequate strength and heat resistance. Thus, this tape is not suited to the steps of forming a TSV and forming a wiring layer on the back surface.
In this context, there has been proposed a system in which a semiconductor substrate is bonded to a support made of silicon, glass or the like, through an adhesive layer to sufficiently withstand the steps of grinding the back surface and forming a TSV and an electrode on the back surface. In this system, the adhesive layer used for bonding the substrate to the support is important. The adhesive layer requires a sufficient durability to bond the substrate and the support without gaps and to withstand subsequent steps, and also requires an ability to easily detach a thin wafer from the support finally. The adhesive layer, which is finally removed, is hence referred to as “temporary adhesive layer” (or temporary adhesive material layer) herein.
With respect to the conventionally known temporary adhesive layer and a method for removing this layer, the following techniques have been proposed: an adhesive material containing a light-absorbing substance is irradiated with high intensity light to decompose the adhesive material layer, whereby the adhesive material layer is removed from the support (Patent Literature 1); a heat fusible hydrocarbon compound is used for the adhesive material, and bonding and removal are carried out in a heat-molten state (Patent Literature 2). The former technique has problems of requiring expensive tools such as laser, and a long treatment time per substrate. The latter technique is simple because of control only by heat, but thermal stability is insufficient at a high temperature exceeding 200° C., and thus the applicable range is limited. Furthermore, these temporary adhesive layers are not adequate to form a film with uniform thickness on a heavily stepped substrate and to provide a complete adhesion to the support.
Moreover, it has been proposed to use a silicone pressure sensitive adhesive for the temporary adhesive material layer (Patent Literature 3). In this technique, a substrate is bonded to a support with an addition-curable silicone pressure sensitive adhesive, and on the removal, the assembly is immersed in a chemical solution capable of dissolving or decomposing the silicone resin to separate the substrate from the support. Thus, this method takes a very long time for separation and is difficultly applied to the actual producing process. Moreover, a method of applying a liquid composition by spin coating and removing a solvent to form a resin layer on the wafer has problems of decrease in yield and increase in cost.
Moreover, it has been proposed to use a silicone adhesive for semiconductor (Patent Literature 4). However, this technique causes cracks when the adhesive is formed into a film on a protective film due to an extremely high elastic modulus after curing, thus failing in lamination process.